The present application is primarily concerned with the adaptation of many features of the parent applications referred to above to existing trucks. By virtue of such adaptation or "retrofitting", it is not necessary, in order to utilize features of the invention, to completely replace existing railroad trucks.
The adaptation or "retrofit" arrangements to which the present application is directed thus have much background, objects and advantages in common with the arrangements of the parent application above referred to; and many of these features are set out herebelow, in addition to the retrofit technique and features, all of which are described and explained fully hereinafter.
While of broader applicability, for example in the field of highway vehicles where use of certain features of the invention can reduce lateral scrubbing of tires as well as lessening the width of the roadway required for negotiating curves, my invention is especially useful in railway vehicles and particularly railway trucks having a plurality of axles. Accordingly, and for exemplary purposes, the invention will be illustrated and described with specific reference to railway rolling stock.
The axles of the railway trucks now in normal use remain substantially parallel at all times (viewed in plan). A most important consequence of this is that the leading axle does not assume a position radial to a curved track, and the flanges of the wheels strike the curved rails at an angle, causing objectionable noise and excessive wear of both flanges and rails.
Much consideration has been given to the avoidance of this problem, notably the longstanding use of wheels the treads of which have a conical profile. This expedient has assisted the vehicle truck to negotiate very gradual curves.
However, as economic factors have led the railroads to accept higher wheel loads and operating speeds, the rate of wheel and rail wear becomes a major problem. A second serious limitation on performance and maintenance is the result of excessive, and even violent, oscillation of the trucks at high speed on straight track. In such "nosing", or "hunting", of the truck the wheelsets bounce back and forth between the rails. Above a critical speed hunting will be initiated by any track irregularity. Once started, the hunting action will often persist for miles with flange impact, excessive roughness, wear and noise, even if the speed be reduced substantially below the critical value.
In recent efforts to overcome the curving problem, yaw flexibility has been introduced into the design of some trucks, and arrangements have even been proposed which allow wheel axles of a truck to swing and thus to become positioned substantially radially of a curved track. However, such efforts have not met with any real success, primarily because of lack of recognition of the importance of providing the required lateral restraint, as well as yaw flexibility, between the two wheelsets of a truck, to prevent high speed hunting.
For the purposes of this invention, yaw stiffness can be defined as the restraint of angular motion of wheelsets in the steering direction, and more particularly to the restraint of conjoint yawing of a coupled pair of wheelsets in a truck. The "lateral" stiffness is defined as the restraint of the motion of a wheelset in the direction of its general axis of rotation, that is, across the line of general motion of the vehicle. In the apparatus of the invention, such lateral stiffness also acts as restraint on differential yawing, of a coupled pair of wheelsets.
The above-mentioned general problems produce many particular difficulties all of which contribute to excessive cost of operation. For example, there is deterioration of the rail, as well as widening of the gauge in curved track. In straight track the hunting, or nosing, of the trucks causes high dynamic loading of the track fasteners, and of the press fit of the wheels on the axles, with resultant loosening and risk of failure. A corresponding increased cost of maintenance of both trucks and cars also occurs. As to trucks, mention may be made, by way of example, to flange wear and high wear rates of the bolster and of the surfaces of the side framing and its bearing adapters.
As to cars, there occurs excessive center plate wear, as well as structural fatigue and heightened risk of derailment resulting from excessive flange forces. The effects on power requirements and operating costs, which result from wear problems of the kinds mentioned above, will be evident to one skilled in this art.
In brief, the lack of recognition of the part played by yaw and lateral stiffness has led to: (a) flange contact in nearly all curves; (b) high flange forces when flange contact occurs; and (c) excessive difficulty with lateral oscillation at high speed. The wear and cost problems which result from failure to provide proper values of yaw and lateral stiffness, and to control such values, will now be understood.
It is the general objective of my invention to overcome such problems by the use of self-steering wheelsets in combination with novel apparatus which maintains stability at speed, and to this end I utilize an articulated, self-steering, truck having novelly formed and positioned elastic restraint means which makes it possible to achieve flange-free operation in gradual curves, low flange forces in sharp curves, and good high speed stability.
I have further discovered that application of certain principles of this invention to highway vehicles not only reduces tire scrubbing and highway space requirements, as noted above, but also promotes good stability at high speed.
To achieve these general purposes, and with particular reference to railway trucks, the invention provides an articulated truck so constructed that: (a) each axle has its own, even individual, value of yaw stiffness with respect to the truck framing; (b) such lateral stiffness is provided as to ensure the exchanging of steering moments properly between the axles and also with the vehicle body; and (c) the proper value of yaw stiffness is provided between the truck and the vehicle.
An embodiment representative of the invention has been tested at nearly eighty miles per hour, with virtually no trace of instability. With another embodiment, radial curving has been observed at less than 50 foot radius, and flange-free operation is readily achieved with all embodiments on curves of at least 4 degrees.
With more particularity, it is an objective flexibly to restrain yawing motion of the axles by the provision of restraining means of predetermined value between the side frames and the steering arms of a truck having a pair of subtrucks coupled through steering arms rigidly supporting the axles. Elastomeric means for this purpose are provided between the axles and the adjacent side frames, preferably in the region of the bearing means. Such means may be provided at one or both axles of the truck. If provided at both axles, it may have either more or less restraint at one axle, as compared with the restraint at the other, depending upon the requirements of the particular truck design.
It is a further object of this invention to provide elastomeric restraining means in the region of the coupling between the arms to damp lateral axle motions, which results in so-called "differential" yawing of a coupled pair of subtrucks.
The invention is also featured by certain tow bar improvements which take care of longitudinal forces between the car body and the flexibly mounted wheelsets. This arrangement has several advantages, discussed hereinafter, one of which is to prevent excessive deflections, in the elastomeric pads which mount the steering arms to the side frames and the side frames to the car body.
In accordance with another feature of the invention, a special sliding bearing surface is provided between the truck side frames and the car body, further to limit the flange forces in very sharp curves.
My invention also contemplates brake improvements which, when used in conjunction with articulated trucks characteristic of this invention, virtually eliminate contact of the brake shoes with the wheel flanges. Prior to the invention such contact has resulted in substantial wear and in uneven braking.
An important feature of the present invention is the provision of a novel technique for retrofitting existing trucks to provide for the steering of the wheelsets. Thus, an important characteristic of this invention is the fact that it may readily be applied to existing trucks, for example to the 100 ton roller bearing, freight truck design of the Association of American Railroads. Accordingly, one embodiment of the invention, herein disclosed and claimed, teaches the retrofitting of the AAR truck with self-steering wheelsets combined with the stabilizing elastomeric coupling and restraining means characteristic of my invention.